This invention relates to molten metal reactors for treating waste materials and soils contaminated with waste materials. More particularly, the invention relates to a molten metal reactor having an improved arrangement for entraining or entrapping feed materials with a molten reactant metal to effect the desired chemical reduction of the feed material. The invention encompasses a molten metal reactor apparatus, a structure for introducing a feed material into such a reactor, a method for treating waste material with a molten metal, and a method for introducing a feed material into a molten metal reactor.
Molten metal reactors utilize a molten reactant metal to chemically react with a feed material in order to reduce the feed material to relatively innocuous compounds and chemical elements. For example, U.S. Pat. No. 5,000,101 to Wagner discloses a molten metal reactor for treating chlorinated hydrocarbons and other dangerous organic chemicals to produce carbon, metal salts, and gases such as nitrogen and hydrogen. U.S. Pat. No. 5,271,341 to Wagner discloses a molten metal reactor for treating boxed biomedical wastes which may include hazardous biological wastes mixed with other materials and metals. The disclosed molten reactant metal chemically reduces biological materials and other organic materials in this waste to carbon, metal salts and elemental gasses. Metals such as stainless steel xe2x80x9csharpsxe2x80x9d in the waste dissolve or melt into the reactant metal.
A consistent issue with molten metal reactors is providing the necessary contact between the material to be treated or reacted, that is, the xe2x80x9cfeed material,xe2x80x9d and the molten reactant metal. U.S. Pat. No. 5,271,341 to Wagner discloses submerging the boxed biomedical wastes in the reactant metal bath with a submerging or plunger structure to provide the desired contact between the waste material and the molten reactant metal. Although the submerging structure works well with certain types of waste materials, such structures are not well suited for submerging other types of materials. In particular, plunger structures are not well suited for use in relatively high-volume waste treatment applications in which relatively large quantities of loose or bulk feed materials, such as contaminated soils, for example, must be processed.
A molten metal reactor according to the present invention quickly entrains a feed material in the molten reactant metal and provides the necessary contact between the molten reactant metal and the feed material to effect the desired chemical reduction of the feed material. The quick entrainment of feed material in the molten reactant metal is accomplished with a unique feed structure in which the feed material is added to the reactant metal and then quickly transferred into a treatment chamber together with the molten reactant metal and any initial reaction products. A majority of the desired reactions occur in the treatment chamber. Reaction products and unspent reactant metal are preferably directed from the treatment chamber to an output chamber where reaction products are removed from the reactor. Unspent reactant metal is then preferably transferred to a heating chamber where it is reheated for recycling through the system.
According to the invention, the feed structure associated with the reactor introduces feed material into the molten reactant metal so that a flow of molten reactant metal immediately carries substantially all of the feed material and any initial reaction products into the treatment chamber. The feed material and reaction products are then trapped in the treatment chamber preferably by means of a suitable gravity trap structure. This combination of substantially immediate introduction into the treatment chamber and trapping in the treatment chamber helps ensure that the feed material and any intermediate reaction products have sufficient contact with the molten reactant metal to provide the desired chemical reactions, that is, the substantially complete chemical reduction of the feed material.
The desired contact with the reactant metal is enhanced according to the invention by inducing a swirling or vortex flow in the molten reactant metal in a feed chamber in which the feed material first makes contact with the molten reactant metal. This swirling flow may be produced in any suitable fashion, including by directing the molten metal into the feed chamber in an off center position, by driving the molten metal in the feed chamber with an impeller, or both. Also, a bowl-shaped feed chamber helps facilitate the desired swirling flow.
In order to carry the feed material and any initial reaction products quickly into the treatment chamber in the flow of molten reactant metal, the feed material preferably comes into contact with the molten reactant metal in an area adjacent to an inlet to the treatment chamber. An area xe2x80x9cadjacentxe2x80x9d to the treatment chamber inlet means the area of the surface of the molten reactant metal in the feed chamber generally nearest to the inlet of the treatment chamber. In the form of the invention in which a swirling flow is induced in the feed chamber, the feed material drops into the molten reactant metal in a central area of the feed chamber, at the center of the swirling flow or vortex, and directly above an outlet from the feed chamber/inlet to the treatment chamber. The feed chamber includes an outlet that at least borders the treatment chamber inlet and more preferably comprises a common opening with the treatment chamber inlet. By xe2x80x9cborderingxe2x80x9d the treatment chamber inlet it is meant that the feed chamber outlet is in the immediate vicinity of the treatment chamber inlet so that there is only a small distance between any point of the feed chamber outlet and any point of the treatment chamber inlet.
The feed material may include substantially any material or mixture of materials suitable for treatment in a molten metal reactor. These materials include hydrocarbons and halogenated hydrocarbons, low and high level radioactive materials, and any other materials that may be chemically reduced in a molten reactant metal such as aluminum, magnesium, or combinations of these metals together with other metals. The invention is particularly suited to treating soils and other bulk solids which have been contaminated with hydrocarbons, halogenated hydrocarbons, other chemically reducible materials, radioactive materials, and metals. As used in this disclosure and the accompanying claims a xe2x80x9cfeed materialxe2x80x9d may comprise any of the above-described materials or combinations of these materials.
It will be appreciated by those skilled in the art of molten reactors that the chemical reduction reactions produced by contact with a molten reactant metal may not immediately reduce a given constituent compound included in a feed material. Rather, many chemical compounds suitable for treatment with a molten reactant metal may initially react in or with the metal to produce intermediate reaction products. These intermediate reaction products are then further reduced by reaction in or with the molten reactant metal. The reactions continue in the molten reactant metal until the reduction reactions are substantially complete, leaving only final reaction products. Metals in the feed material compounds are generally reduced to their elemental state, carbon is reduced to its elemental state and goes to a gaseous state at the temperature of the molten reactant metal, halogens form salts with either metals from the molten reactant metal bath or with metals contained in the feed material itself. Nitrogen and hydrogen liberated from the reacted compounds escape from the molten metal bath as gases. Minerals included in soil generally remain unreacted in the molten reactant metal depending upon the makeup of the molten reactant metal bath and its temperature, but may go to a liquid state at the temperature of the molten metal bath.
As used in this disclosure and the accompanying claims, the term xe2x80x9creaction productxe2x80x9d is used to refer to any reaction product produced by treatment of the feed material with the molten reactant metal, whether the reaction product is an initial reaction product subject to further reactions in the molten metal or a final reaction product that is chemically stable in the molten reactant metal. The term xe2x80x9creaction productxe2x80x9d also refers to materials such as quartz that do not chemically react with the molten reactant metal but may be contained in soil contaminated with materials that do react in the molten reactant metal. Thus, the term xe2x80x9creaction productxe2x80x9d means generally any material that results from any reaction of a feed material occurring in the molten reactant metal.
The above-described advantages and features of the invention, along with other advantages and features, will be apparent from the following description of the preferred embodiments, considered along with the accompanying drawings.